Molecular Chain Structure Research Articles

Compositional Analysis of an Impact Polypropylene Copolymer by Fast Scanning DSC and FTIR of TREF-SEC Cross-Fractions

For the first time, the complex composition of a two-reactor-produced impact polypropylene copolymer (IPC) has been fully revealed by advanced thermal analysis, using the combination of fast scanning DSC (HPer DSC, flash DSC, and solution DSC) with SEC fractionation subsequent to TREF fractionation. The dual TREF-SEC separation provided fractions of a few micro- or nanograms that were used to correlate the molecular structure of the polymer chains and their thermal properties (melting and crystallization behavior of the different macromolecules under a variety of different conditions). The SEC fractions were collected using the LC transform interface and subjected to FTIR and fast scanning DSC analysis. The SEC curves showed mono-, bi-, and multimodal molar mass distributions. The SEC fractions collected were analyzed by HPer DSC at 50 °C/min by which the thermal properties of the fractions could be established and salient details revealed. The findings were confirmed by structural information that was ob...

Hybrid molecular nanostructures with donor-acceptor chains

We have fabricated hybrid molecular chain structures formed by electron acceptor compound 1 and electron donor molecules 2 and 3 at the liquid/solid interface of graphite surface. The structural details of the mono-component and the binary assemblies are revealed by high resolution scanning tunneling microscopy (STM). Compound 1 can form two well-ordered lamellar patterns at different concentrations. In the co-adsorption structures, compounds 2 and 3 can insert into the space between molecular chains of compound 1 and form large area well-ordered nanoscale phase separated lamellar structures. The unit cell parameters for the coassemblies can be “flexibly” adjusted to make the electron donors and acceptors perfectly match along the molecular chains. Scanning tunneling spectroscopy (STS) results indicate that the electronic properties of individual molecular donors and acceptors are preserved in the binary self-assembly. These results provide molecular insight into the nanoscale phase separation of organic electron acceptors and donors on surfaces and are helpful for the fabrication of surface supramolecular structures and molecular devices.

Study on the Preparation of Micro-Emulsified Diesel Oil and its Influencing Factors

In this experiment, the micro-emulsified diesel oil is prepared by using alkanol amide from the reaction between oleic acid and ethanolamine and the mixture of them and with its by-products as the surfactant and alcohols with different carbon chain lengths and molecular structures as the co-surfactant. The experiment explores the effect of the proportion and dosage of the surfactant on the water solubilization, studies the influence of the category, construction and dosage of the co-surfactant on the water solubilization and its stability, and also discusses the impact of concentration of the electrolyte on the micro-emulsion. The experimental result shows that the no1-ionic surfactant can be used to prepare the W/O micro-emulsified diesel oil when this is satisfied: m (oleic acid): m (ethanol amine) =10:1 and that 1-pentanol, isoamyl alcohol, 1-hexanol, benzyl alcohol can all be used as its co-surfactant. The co-surfactant of benzyl alcohol or 1-pentanol helps to ensure its mechanical and temperature stability, and to prepare the micro-emulsified diesel oil with no1-ionic surfactant from the reaction between oleic acid and ethanolamine as surfactant, one of the best formulation should be like this: room temperature(20°C），ω（0 # diesel oil）=70.6%, ω（surfactant）=9.2%, ω（benzyl alcohol）=5.0%, ω（inorganic salt solution）=15.2%.

Octithiophene on Cu(111) and Au(111): Formation and Electronic Structure of Molecular Chains and Films

Adsorption and electronic structure of octithiophene (8T) molecules on Cu(III) and Au(III) surfaces are investigated using scanning tunneling microscopy (STM) and spectroscopy (STS) at room temperature. We find a large difference in adsorption behavior of 8T molecules on the two surfaces. At the initial stage of adsorption, 8T molecules are stabilized in the form of molecular chain on a terrace of Cu(III), whereas neither such chain structure nor isolated 8T molecules have been observed on a terrace of Au(III). By increasing the amount of adsorbed molecules, a disordered monolayer film is formed on Cu(III) while a well-ordered monolayer film is formed on Au(III). From the spectroscopic investigations using bias-dependent STM images and STS spectra and by comparing the data with theoretical calculations, it is found that the electronic property of 8T molecules in the molecular chain on Cu(III) is different from that of a free-standing 8T molecule while that in the monolayer film on Au(III) keeps original character of the free-standing 8T molecule. The present study shows that adsorption of 8T molecules on Cu(III) results in a formation of adsorption-induced states near the Fermi level.

Design and Synthesis of Self-Degradable Antibacterial Polymers by Simultaneous Chain- and Step-Growth Radical Copolymerization

Self-degradable antimicrobial copolymers bearing cationic side chains and main-chain ester linkages were synthesized using the simultaneous chain- and step-growth radical polymerization of t-butyl acrylate and 3-butenyl 2-chloropropionate, followed by the transformation of t-butyl groups into primary ammonium salts. We prepared a series of copolymers with different structural features in terms of molecular weight, monomer composition, amine functionality, and side chain structures to examine the effect of polymer properties on their antimicrobial and hemolytic activities. The acrylate copolymers containing primary amine side chains displayed moderate antimicrobial activity against E. coli but were relatively hemolytic. The acrylate copolymer with quaternary ammonium groups and the acrylamide copolymers showed low or no antimicrobial and hemolytic activities. An acrylate copolymer with primary amine side chains degraded to lower molecular weight oligomers with lower antimicrobial activity in aqueous solution. This degradation was due to amidation of the ester groups of the polymer chains by the nucleophilic addition of primary amine groups in the side chains resulting in cleavage of the polymer main chain. The degradation mechanism was studied in detail by model reactions between amine compounds and precursor copolymers.

Determination of Phase Content in Multiphase Polymers by Solid-State NMR Techniques

Solid-state nuclear magnetic resonance (NMR) spectroscopy has emerged as a relatively facile technique for the characterization of multi-component polymer systems. In particular, it has emerged to be a useful technique for probing the molecular structure, conformation and dynamics of polymer chains at interfaces between phases in various types of multi-component polymer systems including nanomaterials. The usefulness of solid-state NMR stems from its ability to non-destructively probe not only the bulk of the polymer, but moreover its ability to selectively probe the interface or interphase. As such, the technique has been extensively exploited in the study of multi-component polymer systems. To achieve 13C spectral resolution in the solid-state magic angle spinning (MAS), dipolar decoupling and cross-polarization are applied which enables the study of individual carbon atoms directly with excellent resolution and sensitivity. Some examples of applications of this technique to the study of multiphase aliphatic polyesters are reviewed herein.

Microstructure, Rheology, and Potential Oil Absorbency of Poly(Butyl Methacrylate) and Poly(Hydroxyethyl Methacrylate) Blends

To prepare oil-absorptive polymers with moderate cross-linking structure, poly(butyl methacrylate) (PBMA) was synthesized as a linear hydrophobic polymer by suspension polymerization. In addition, hydroxyethyl methacrylate (HEMA), as a monomer, which could construct a network structure among the macromolecules via hydrogen bond interactions, was solution polymerized in dimethylacetamide (DMAc) with PBMA, yielding a polymer blend of PBMA and PHEMA. The solution of the polymer blend was investigated by rotational viscometry and extended rheometry. The results showed that the viscosity varied greatly with the temperature and shear rate for three different compositions. Fourier transform infrared (FTIR) spectra indicated that an entanglement or interlocking cross-linking structure of molecular chains was constructed by hydrogen bonds. The results from nuclear magnetic resonance (NMR) spectra exhibited a downfield movement of the proton peak as influenced by end groups or hydroxyls in the polymer chains. The rheological measurements demonstrated that the cross-linking structure greatly affected the rheological behavior of the blend solution. In addition, the cross-linking structure was also evaluated by oil absorbency of films.

Preparation and Characterization of Konjac Glucomannan Gel

Konjac glucomannan (KGM) gel was prepared by alkali catalyzed in aqueous solutions. The structure of the KGM gel was characterized by Fourier transform infrared (FTIR) spectroscopy and wide angle X-ray diffraction (WAXRD). The gel point of KGM solutions was determined by steady state fluorescence method and It was observed that the gel point of the KGM solutions depend on the concentration of KGM, pH value and temperature effectively. The results showed that the molecular chain structure of KGM gel is more regular than that of the pure KGM.

Structure determination of the nonlinear hydrocarbon chains C9H3 and C11H3 by deuterium labeling

A systematic deuterium labeling experiment is presented that aims at an unambiguous determination of the geometrical ground state structure of the C(9)H(3) and C(11)H(3) hydrocarbon chains. Cavity ring-down spectroscopy and special plasma expansions constituting C/H, C/D, and C/H/D are used to record optical transitions of both species and their (partially) deuterated equivalents in the 19,000 cm(-1) region. The number of observed bands, the quantitative determination of isotopic shifts, and supporting calculations show that the observed C(9)H(3) and C(11)H(3) spectra originate from HC(4)(CH)C(4)H and HC(4)[C(C(2)H)]C(4)H species with C(2v) symmetry. This result illustrates the potential of deuterium labeling as a useful approach to characterize the molecular structure of nonlinear hydrocarbon chains.

Preparation and characterization of silicon oil based ferrofluid

Stable silicon oil based ferrofluid was prepared in the present investigation. Silicon oil surfactant ethoxy terminated polydimethylsiloxane was used to modify the Fe 3O 4 nanoparticles. The Fe 3O 4 nanoparticles were firstly coated with a SiO 2 layer by the hydrolysis of tetraethoxysilane. Then using the active hydroxyl groups on the surface of the SiO 2, silicon oil surfactant was covalently grafted onto the Fe 3O 4 nanoparticles surface. The ethoxy terminated polydimethylsiloxane has similar molecular chain structure and good compatibility with that of the carrier liquid, thus ensuring stable dispersion of modified Fe 3O 4 in the carrier silicon oil. The interaction between Fe 3O 4 and the modifier was characterized by IR and XPS. The crystal structure and the magnetic properties of the Fe 3O 4 nanoparticles were determined by XRD and VSM, respectively. The size and morphology of the particles were observed using TEM. The properties of the silicon oil based ferrofluid were characterized by Gouy magnetic balance. The results indicated that the ferrofluid had high magnetism and good stability. The rheological properties and thermostability of the ferrofluid were also investigated.

EFFECT OF SELECTIVE SOLVENTS FOR B BLOCK ON SURFACE SEGREGATION OF FLUORINE-CONTAINING ABC TRIBLOCK COPOLYMERS

Novel ABC triblock copolymers of poly(methyl methacrylate)-b-poly(n-butyl methacrylate)(or n-octadecyl methacrylate)-b-poly(2-perfluorooctylethyl methacrylate)(PMMA230-b-PBMA12(or PODMA12)-b-PFMAn) were synthesized by atom transfer radical polymerization(ATRP).The effect of selective solvents on surface structure of the triblock copolymers film was investigated by X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD) and dynamic light scattering(DLS).The higher surface enrichment of fluorinated moieties in PMMA230-b-PBMA12-b-PFMA1 was found as the film was cast by cyclohexanone solution,compared to the film cast by toluene solution.When the length of PFMA units was about 4,the ratio of fluorine to carbon was nearly the same.As for PMMA230-b-PODMA12-b-PFMAn,the fluorinated moieties can segregate more easily on the surface as the film was cast with toluene solution,compared to the film cast from cyclohexanone solution.The reason could be attributed to the difference in compatibility between solvent and the middle block in triblock copolymers,which would affect the stability of triblock copolymers micelle in various solutions.When the solvent was the good solubility for the middle block chain,there were unstable and loose packed micellar aggregates in solution.The unstable micelle of the triblock copolymer in solution was in favor of fluorine segregation on the surface during film-formation.During film formation,the perfluoroalkyl side chains can easily segregate to the surface and be packed in a well-ordered manner,resulting in enhanced surface enrichment of fluorine element.The results suggest that copolymer solution properties,may play an important role in structure formation on the solid surface,in addition to for the molecular chain structures of copolymers.

The synthesis of novel perylene-like dyes and their aggregation properties in Langmuir and Langmuir–Blodgett films

The synthesis of novel perylene-like dyes with different length and molecular structure of terminal chains substituted to the main perylene core is described. The dyes are able to form compressible and stable monolayers at the air–water interface (Langmuir films), which can be easily transferred onto solid substrates (Langmuir–Blodgett films). In the Langmuir and Langmuir–Blodgett films, the dye molecules show tendency to creation of self-aggregates, both in the ground and excited electronic states. The influence of the molecular structure of the substituents on the aggregation properties is observed and discussed.

Initial stage of adsorption of octithiophene molecules on Cu(111)

The initial stage of the adsorption of octithiophene (8T) molecules on a Cu(111) surface is investigated using a scanning tunneling microscope at room temperature. We find a characteristic molecular chain structure of 8T molecules on a terrace of the Cu(111) surface, which has not been reported so far for adsorption of oligothiophene molecules on metal surfaces. Up to the adsorption of 0.26 monolayer (ML), 8T molecules in the molecular chain align with their long axis parallel to the Cu<11-2> direction. With increasing coverage, there appear 8T molecules that align with their long axis parallel to the Cu<110> direction. The appearance of different molecular orientations is understood by the decrease of the number of the adsorption sites for extending the molecular chains. Fragments of 8T molecules, such as single thiophene molecules, are also observed in this work. They are trapped only at the step edges of the Cu(111) surface at the beginning and later trapped in a small Cu(111) region surrounded by 8T molecules.

Antioxidants: Its medicinal and pharmacological applications

Antioxidants are essential and important for plants and animals’ sustenance. They are substances that protect cells from the damage caused by unstable molecules known as free radicals. The sources and origin of antioxidants which include fruits and vegetables, meats, poultry and fish were treated in this study. The types of antioxidants such as ascorbic acid, glutathione, melatonin, tocopherols and tocotrienols were reported. The classification and characteristics of antioxidant; its measurements and level in food and free radicals were also documented. The Chemistry of antioxidants which include chain reactions, molecular structures, food antioxidants and reaction mechanisms, bio-chemical activity and effects of antioxidants were also reviewed. Further, the medicinal applications, pharmacological effects, therapeutic properties and future choice of antioxidants were reported in this review.

Large Enhancement in Conductivity of Polyaniline Films by Cold Stretching

AbstractThe hot‐stretching method has been well accepted for enhancing the electrical conductivity of conducting polymer films. High temperature is the prerequisite to soften the polymer to highly align and elongate the polymeric molecular chains. In this study, the cold‐stretching method is proposed for the first time to enhance the conductivity of conducting polymeric films. Polyaniline (PANI) films are stretched at room temperature to different strain levels. It is observed that the applied strain has significant effects on the morphology, molecular chain structure, crystallinity, and crosslinking of the PANI films. As a result, the conductivity of PANI films is effectively increased by the cold‐stretching process. Particularly, a maximum conductivity with an 18.4‐fold increase in the direction parallel to the stretched direction is obtained when the elastic limit strain is applied. Compared to hot stretching, cold stretching is unique due to the extremely low dimensional change and very high efficiency achieved.magnified image

SYNTHESIS OF POLY(ε-CAPROLACTONE)/POLY(ETHYLENE GLYCOL) BLOCK COPOLYMERS AND SURFACE PROPERTY CONTROL OF THEIR MICROSPHERES

A method was developed to synthesize amphiphilic poly(e-caprolactone)-b-poly(ethylene glycol)(PCL-b-PEO) block copolymers with well-defined structure and with functional amino end-group connected to the PEO block.The molecular weight,composition and chain structure of the resultant copolymers were characterized by GPC and()~1H-NMR.The microspheres of the copolymers were prepared by W/O/W double emulsion solvent evaporation method.The analysis results by confocal laser scanning microscopy indicate that the amino groups are distributed dominantly on the surface of microspheres due to the hydrophilic property of amino groups and the formation process of microspheres in aqueous phase.The surface morphology of microspheres could be regulated by changing the composition of block copolymers.The results of this work indicate that the surface properties of the microspheres can be controlled by polymer chain structure,and that the microspheres with amino group located on the surface can be further conjugated with peptide such as RGD.Therefore,these microspheres are promising materials as microcarriers for promoting cell growth.

Morphology and physical properties of a novel Ramie‐PU blended nonwoven by electrospinning: The effect of cosolvent ratio

AbstractA novel macro/nano blended nonwoven with excellent physical properties was prepared by electrospinning polyurethane (PU) nanofibers onto the surface of ramie webs under different weight ratios of N,N‐dimethylacetamide (DMAc)/acetone cosolvents. The ratio of cosolvents has a significant influence on the morphology, tensile properties, resilience, and thermal properties of the resultant samples. Bead‐free and fine interconnected nanofibers were obtained with an increase of acetone content up to 60 wt%. The total physical properties of the blended nonwovens were optimal for a DMAc/acetone ratio of 40/60, in which the tensile load at break, extension at break and Young's modulus were 441, 54, and 256% higher than that of pure ramie web, respectively. The resilience of the blended nonwovens was ∼20% higher than that of nonblended ramie web. The significant improvement of physical properties may be due to the good connection between PU nanofiber membranes and ramie webs and the molecular chain structure differences, interconnected structural differences, and high extensibility of PU nanofibers, according to the results of crystallization by differential scanning calorimetry (DSC) and morphological observation by scanning electronic microscopy (SEM). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1–14, 2010

SHAPE MEMROY EFFECT OF MESOGEN-JACKEDTED LIQUID CRYSTAL POLYMER FIBER

The shape memory effect of poly2,5-bis[(4-butoxyphenyl)oxycarbonyl]-styrenes(PBPCS),one of the classical mesogen jacketed liquid crystal polymers(MJLCPs),fiber was studied by dynamic mechanical analysis(DMA).According to the results,the outstanding shape recovery ability of PBPCS fiber was found.The reversion rate of PBPCS fiber was improved with the increase of temperature apparently when it was above T_g(106.7℃).Especially when temperature above 145℃,the rate of shape recovery was the best.The time of recovery from 400% draw ratio to origin length was about 9 min.The repeatability of shape memory was good in 5 repeated times.2-Dimensional wide angle X-ray diffraction(2D WAXD)experiments showed the diameter of helical cylindrical blocks changed from 2.5 nm to 2.4 nm after deformation.This result indicated that the helical main-chain of PBPCS was in a more straight conformation.So,there would be a certain inner stress in the molecular chain,namely the shape memory force(F_ sm).It was about 1.6 MPa.There was no stable and memory phase structure of traditional shape memory polymers(SMP)in PBPCS because it was an amorphous polymer.The reason of PBPCS fiber with the shape memory effect is its special helical molecular chain structure just as a spring,say,the flexible polystyrene main chain makes PBPCS fiber present a good strain reversion ability,and the mesogenic effect of side chains makes the fiber keep its original dimension.

Hydrogen-Bonded Polymer Nanotubes in Water

Intermolecular hydrogen bonding, not hydrophobic interaction, is the driving force for the spontaneous self-assembly of glycosylated polyoxazoline chains into nanotubes in dilute aqueous solution. The structural information is encoded in the relatively simple molecular structure of chains consisting of a tertiary polyamide backbone (hydrogen-accepting) and glucose side chains (hydrogen-donating). The formation of the nanotubes should occur through bending and closing of a 2D hydrogen-bonded layer of interdigitated polymer chains.

Cationic phospholipids: structure–transfection activity relationships

Synthetic cationic lipids are presently the most widely used non-viral gene carriers. Examined here is a particularly attractive cationic lipid class, triester phosphatidylcholines (PCs) exhibiting low toxicities and good transfection efficiency. Similarly to other cationic lipids, they form stable complexes (lipoplexes) with the polyanionic nucleic acids. A summary of studies on a set of ∼30 cationic PCs reveals the existence of a strong, systematic dependence of their transfection efficiency on the lipid hydrocarbon chain structure: transfection activity increases with increase of chain unsaturation from 0 to 2 double bonds per lipid and decreases with increase of chain length in the range ∼30–50 total number of chain carbon atoms. Maximum transfection was observed for ethyl phosphate PCs (EPCs) with monounsaturated 14:1 chains (total of 2 double bonds and 30 chain carbon atoms). Lipid phase behavior is known to depend strongly on the chain molecular structure and the above relationships thus substantiate a view that cationic PC phase propensities are an important determinant of their activity. Indeed, X-ray structural studies show that the rate of DNA release from lipoplexes as well as transfection activity well correlate with non-lamellar phase progressions observed in cationic PC mixtures with membrane lipids. These findings appear to be of considerable interest because, according to current views, key processes in lipid-mediated transfection such as lipoplex disassembly and DNA release within the cells are believed to take place upon cationic lipid mixing with cellular lipids.